The present invention relates to injection molding and more particularly relates to novel apparatus and methods for liquid injection molding an intraocular lens (“IOL”). Intraocular lenses having a single optic have been known and used for many years. IOL manufacturing has included cast molding, lathing and liquid injection molding (LIM). In the LIM technique, a cold liquid lens material, for example a pre-mixed two-part liquid silicone, is injected into a heated mold cavity of the desired configuration and allowed to cure and harden. While LIM is a cost-effective technique for making intraocular lenses, improvements could be made to various aspects thereof such as, for example, surface finishes and gating designs that do not create unwanted knit lines, gate vestiges and the like.
More recently, accommodating intraocular lens devices having two optics interconnected by one or more haptics have been disclosed in the following U.S. patents and applications to Faezeh Sarfarazi, the entirety of which are incorporated herein by reference:
U.S. Pat. No. 5,275,623 “Elliptical Accommodative Intraocular Lens For Small Incision Surgery”;
U.S. Pat. No. 6,423,094 “Accommodative Lens Formed From Sheet Material”;
U.S. Pat. No. 6,488,708 “Open Chamber Elliptical Accommodative Intraocular Lens System”;
U.S. Ser. No. 10/445,762 filed on May 27, 2003 entitled “Mold for Intraocular Lens”.
The Sarfarazi accommodating lens device includes two optics, one negative and the other positive for placing in the evacuated lens capsule of an eye. The optics are interconnected along their peripheries by one or more haptics which space the optics from each other and assist in properly positioning the device in the eye. The haptics are formed from a flexible material such that they may flex in response to forces exerted by the eye's ciliary muscles which control accommodation. The haptics will thus flex and bow further radially outwardly upon a compressive force being applied to the device, whereby the two optics are drawn closer together to achieve an accommodative effect in the eye. When the ciliary muscles relax, the haptics flex in the opposite direction (toward a straightened position) causing the optics to space further apart and the lens device returns the eye to its natural, unaccommodative state.
As stated above, single optic intraocular lenses have been known and used for decades while the two lens accommodative intraocular lens device is new and not yet seen on the market. It will be appreciated that manufacturing, packaging and otherwise handling a two optic lens device presents issues not present in the manufacture, packaging and handling of single optic intraocular lenses. In the '762 application listed above, a two optic IOL is injection molded in a mold cavity having a removable metal insert centrally located between first and second cavity blocks. The IOL first optic is formed between the first cavity block and a first surface of the mold insert and the second optic is formed between the second cavity block and the opposite surface of the mold insert. The haptics interconnect and are integrally formed with the first and second optics. The inner surfaces of the haptics are formed by the perimeter of the mold insert and the outer surfaces thereof are formed by the first and second cavity blocks. Silicone is injected into the cavity and allowed to cure to form the IOL. The cavity blocks are opened and the mold insert is removed therefrom. The mold insert is preferably connected to a handle to permit easy handling thereof. The IOL remains connected to the mold insert as the mold insert is removed from between the cavity blocks. Since the IOL is made of silicone, it may be removed from the mold insert by carefully stretching it to allow the mold insert to pass between an opening defined between the haptic or haptics. The mold insert is then replaced between the cavity blocks to injection mold another IOL. The injection mold tools are made of suitable materials able to withstand repeated molding cycles.
While the above manufacturing method is satisfactory for injection molding a two optic IOL, improvements may be made. For example, a need exists for a robust liquid injection molding method which produces high quality IOLs. It would also be desirable to have a liquid injection molding apparatus and method that reduces or eliminates knit lines, gate vestiges and the like on the molded IOL such that post-molding processes to remove such molding remnants are likewise reduced or eliminated.